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Summer Research Fellowship Programme of India's Science Academies

Use of spectral lines to study physical conditions in molecular clouds

K Lakshmi Priya

Pondicherry University, Kalapet, Puducherry 605014

Dr K Indulekha

Mahatma Gandhi University, Priyadarsini Hills Post, Kottayam, Kerala 686560

Abstract

Transitions of molecules from one energy state to another give rise to spectral lines. Molecules inside the cold and dark molecular clouds can produce bright molecular emission lines at long wavelengths, due to transitions between rotational and vibrational energy levels. Spectral line observations provide us with information which helps in studying the physical conditions of molecular clouds. Molecular hydrogen the dominant molecule in the molecular clouds is symmetric and produces weak spectral lines. Hence, we rely on other molecules with asymmetric structure to detect the molecular cloud. One such is the methanol molecule with a slight asymmetric top shape. The statistical dispersion of velocities about the mean velocity of methanol clouds showing bright emission in the molecular cloud complex is called velocity dispersion. Microturbulence is a form of turbulence that varies over small distance scales. It is one of the several mechanisms that can cause the broadening of spectral lines in the molecular spectrum. We present the results of the 96.741 GHz spectral line observations of methanol towards the molecular cloud complex, Sagittarius B2. The data is from Sgr B2 3 mm band survey using Mopra telescope taken from Australian Telescope Online archive. The spectrum is generated and studied to know the physical conditions of the molecular cloud complex, Sagittarius B2, using DS9 software and python programing language. The velocity dispersion was calculated from the observations made from the spectral lines. The calculated velocity dispersion is then compared with the virial velocity of the molecular cloud. Also, checked for the presence of microturbulence in the molecular cloud.

Keywords: sagittarius B2, methanol lines, molecular clouds, Mopra telescope, velocity dispersion, microturbulence

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